Circuit interrupter with improved overcenter spring operating mechanism

ABSTRACT

An improved circuit interrupter comprises an operating shaft pivotally movable to move a movable contact structure, an overcenter spring operating mechanism movable by means of a manually operable drive means from a spring discharged position to an overcenter spring charged position, latch means in a latching position for latching the operating shaft until the overcenter spring operating mechanism reaches the overcenter spring charged position and means automatically unlatching the latch means when the overcenter spring operating mechanism reaches the overcenter spring charged position to permit the overcenter spring operating mechanism to drive the movable contact structure to the closed position independent of the manually operable drive means. The latch means may also be a double latch for performing the same latching function during an opening operation. The latch means prevents slow closing and opening operations of the circuit interrupter.

United States Patent [191 Davies Jan. 1, 1974 [75] Inventor:

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: June 7, 1972 [21] Appl. No.: 260,637

Norman Davies, Trafford, Pa.

Primary Eraminer-Robert K. Schaefer Assistant E.raminer-Robert A. Vanderhye A!!0rneyA. T. Stratton et al.

[ 5 7 ABSTRACT An improved circuit interrupter comprises an operating shaft pivotally movable to move a movable contact structure, an overcenter spring operating mechanism movable by means of a manually operable drive means from a spring discharged position to an overcenter spring charged position, latch means in a latching position for latching the operating shaft until the overcenter spring operating mechanism reaches the overcenter spring charged position and means automatically unlatching the latch means when the overcenter spring operating mechanism reaches the overcenter spring charged position to permit the overcenter spring operating mechanism to drive the movable contact structure to the closed position independent of the manually operable drive means. The latch means may also be a double latch for performing the same latching function during an opening operation. The latch means prevents slow closing and opening operations of the circuit interrupter.

PATENTED JAN 1 1974 SHEET 1 0F 7 FIG. I

PATENTED JAN 1 I974 SHEET 2 BF 7 FIG. 2

FATENTEDJM new I 3783214 saw an: 7

PATENIED JAN 1 I974 PATENTEUJAR 1 m4 mdE PATENTEUJAR 1 I974 SHEEIHF 7 If) (D NQE.

6 E v V V CIRCUIT INTERRUPTER WITH IMPROVED OVERCENTER SPRING OPERATING MECHANISM CROSS-REFERENCE TO RELATED APPLICATION Certain aspects of the herein disclosed circuit interrupter are disclosed in the application of Norman Davies, Ser. No. 106,328, filed Jan 14, 1971, now US. Pat. No. 3,684,848.

BACKGROUND OF THE INVENTION 1. Field of the Invention:

Circuit interrupters of the type comprising an over center spring operating mechanism.

2. Description of the Prior Art:

In the patent to Gamel et al, Patent No. 3,045,083, there is disclosed a circuit interrupter comprising an operating mechanism with a closing spring and manually operable drive means for driving the closing spring to a compressed charged position while the operating mechanism is latched. The interrupter comprises means for releasing the latch when the spring is charged whereupon the spring discharges to drive the mechanism to thereby move the contacts into the closed position. Separate spring means is provided for opening the contacts. The circuit interrupter of this invention is a simplified structure comprising a single overcenter spring structure for both opening and closing the circuit interrupter, simplified latch means for latching the mechanism until the overcenter spring is in the charged condition and latch releasing means operable by the same continuous motion of the manually operable drive means for releasing the latch and means when the overcenter spring has reached the springcharged position.

SUMMARY OF THE INVENTION The hereindisclosed circuit interrupter comprises a stationary contact structure and a movable contact structure cooperable with the stationary contact structure. An operating shaft is pivotally supported and movable between open and closed positions to move the movable contact structure between open and closed positions. An operating spring structure, comprising an overcenter spring, is movable in one direction from a spring discharged open position to a spring charged open position to charge the opening spring and thereafter the charged opening spring discharges to move the overcenter spring structure from the spring charged open position to a spring discharged closed position to move thevoperating shaft to the closed position. The overcenter spring structure is movable in the opposite direction from the spring discharged closed position to a spring charged closed position to charge the overcenter spring and thereafter the charged overcenter spring discharges to move the overcenter spring structure from the spring charged closed position to the spring discharged open position to move the operating shaft to the open position. Manually operable drive means is mounted on the operating shaft for pivotal movement relative to the operating shaft. The manually operable drive means is manually operable in a first direction to move the overcenter spring structure from the spring discharged open position to the spring charged open position and in a second direction to move the overcenter spring structure from the spring discharged closed position to the spring charged closed position. A spring biased latch member is pivotally mounted on a fixed pivot and biased into latching engagement with the operating shaft when the operating shaft is in the open position to thereby latch the operating shaft in the open position. Upon movement of the manually operable drive means to the spring charged open position the manually operable drive means engages the latch member to move the latch member from the latching position to an unlatching position to thereby unlatch the operating shaft to effect a closing operation of the circuit interrupter. The manually operable drive means is operable with a continuous motion to charge the spring and release the latch member to effect a closing operation of the circuit interrupter. In another embodiment, the latch means comprises a pair of latch members biased against the operating shaft to latch the operating shaft during both closing and opening operations of the circuit interrupter with the manually operable drive means engaging the latch member to unlatch the operating shaft when the spring is charged during both closing and opening operations.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of a circuit interrupter constructed in accordance with the principles of this invention;

FIG. 2 is a side elevational view of the circuit interrupter seen in FIG. 1; I

FIG. 3 is an enlarged front view, with parts broken away, illustrating the operating mechanism seen in FIG.

FIG. 4 is a sectional view taken generally along the line IVIV of FIG. 1 with the closed position of the circuit interrupter being indicated by broken lines;

FIG. 5 is an enlarged side sectional view, with parts broken away, illustrating the position of the parts of the operating mechanism in the spring discharged open position;

FIG. 6 is a view similar to FIG. 5 illustrating the spring-charged open position reached during a closing operation of the circuit interrupter;

FIG. 7 is a view similar to FIG. 5 with the parts being shown in the spring discharged closed position; and

FIG. 8 is a sectional view of the operating shaft and latch meansof another embodiment of the invention wherein the latch means latches the operating shaft during both closing and opening operations.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, there is shown, in FIGS. 1 and 2, a circuit interrupter 7 comprising support means 9 and a circuit interrupter structure 11 supported on the support means 9. The support means 9 comprises a plurality of metallic channel support members and a plurality of plate members secured together to support the various parts of the circuit interrupter structure 1 1. The circuit interrupter structure 11 comprises three stationary contacts 13 (FIGS. 1 and 5) supported on three spaced insulating members 15 that are, -in turn, supported on a back support channel member 17. A separate movable contact arm 19 is provided to cooperate with each of the stationary contacts 13. Each of the contact arms 19 comprises a pair of spaced contact members (FIG. 1) that comprise contact portions that engage the associated sidesof the associated stationary contact 13 in the closed position of the contacts. Each of the contacts arms 19 is supported for pivotal movement on a separate conducting terminal 21 by means of a pivot pin 23. Each of the conductors 21 is supported on an insulating support 25 that is, in turn, supported on another back support channel member 27. In each pole unit a terminal connector 29 is connected to the associated conductor 21 and a terminal connector 31 is connected to the associated stationary contact 13 to enable connection of the pole unit in an electric circuit.

In each pole unit, an elongated rod 33 (FIG. 4) is pivotally connected at one end thereof to the associated movable contact arm 19 by means of a pivot pin 35 and at the other end thereof to a member 37 by means of a pivot pin 39. Each of the members 37 is welded or otherwise fixedly secured to a commonoperating shaft 41. The common operating shaft 41 has reduced end portions that are supported in bearing plates 43 (FIGS. 1 and 3) that are, in turn, secured to elongated side channel support members 45 so that the operating shaft 41 is supported for pivotal movement about the elongated axis thereof on the bearing plates 43. The circuit interrupter is shown in full lines in the open position in FIG. 4. Upon clockwise movement of the operating shaft 41 and members 37 from the open position seen in full lines to the closed position indicated by the broken lines, the three rods 33 are moved to move the three contact arms 19 from the open position shown in full lines to the closed position shown in broken lines. Reverse or counterclockwise movement of the operating shaft 41 and members 37 moves the movable contact arms, through the rods 33, from the closed po sition shown in broken lines to the open position shown in full lines. In the closed position of the contacts, the two parallel members of each of the contact arms 19 straddles each associated knifeblade type stationary contact 13 in a well-known manner.

An operating mechanism 49 (FIGS. 1, 3 and 5-7) is provided for operating the operating shaft 41 between the closed and open positions. The operating mechanism 49 comprises manually operable drive means 51, an overcenter spring structure 53, and a latch member 55. The operating mechanism 49 also comprises a member 57 that is pinned to and fixedly secured to the operating shaft 41 to move the operating shaft 41 as part of the operating shaft 41. The manually operable drive means 51 comprises a handle part 61 that extends through an opening 63 in a front plate member 65 to permit manual operation of the circuit interrupter. The manually operable drive means 51 also comprises a first arm portion 67 and a second arm portion 69. The member 57 comprises a first arm portion 71 and a second arm portion 73. The member 57 also comprises a latch part 75 that is engaged by the latch (FIG. 5) to latch the operating shaft 41. The latch 55 is supported for pivotal movement on a pin 77 that is in turn supported on the plate 43 (FIG. 3). A tension spring 79 (FIGS. 5-7 is connected at one end to the latch 55 and at the other end to a stationary support plate 81 to bias the latch 55 in a clockwise direction to the latching position seen in FIG. 5. A projection 83 is secured to the latch 55 to provide for unlatching of the latch 55 in a manner to be hereinafter described. The drive means 51 is mounted on the operating shaft 41 for pivotal movement relative to the operating shaft 41 about the same axis as the operating shaft 41.

The overcenter spring structure 53 (FIGS. 3 and 5) comprises an arm portion 85 that is pivotally supported on the operating shaft 41 to move relative to the operating shaft 41. As can be understood with reference to FIG. 3, the arm part 85 is provided with a pair of spaced end parts, and an elongated pin 87 extends through openings in the end parts to move with the arm part 85. An elongated rod 89 is provided with an opening therein that receives the pin 87, and the rod is positioned between the spaced end parts of the arm part 85 whereby the one end of the rod 89 is pivotally connected to the arm part 53 of the overcenter spring structure 53. As can be understood with reference to FIG. 5, the rod 89 extends through an opening 91 in a stationary support plate member 93. A compression spring 95 is supported on the rod 89. The spring 95 engages the plate 93 at one end thereof and a washer member or spring support member 97 at the other end thereof. The member 97 is fixedly secured to the operating rod 89, and a pin 99 prevents movement of the spring support member 97 to the right as seen in FIG.

The operation of the circuit interrupter will be best understood with reference to FIGS. 2 and 4-7. The circuit interrupter is shown in FIGS. 2, 4 and 5, in the spring discharged open position. In order to close the circuit interrupter, the handle 61 of the manually operable drive means 51 is rotated in a clockwise direction (FIG. 5) on the operating shaft 41 which is latched in the open position seen in FIG. 5 by means of the latch member 55. During this movement, the arm portion 67 (FIG. 5) of the drive means 51, engaging the pin 87, moves the overcenter spring structure 53 from the spring discharged open position seen in FIG. 5 to the overcenter spring-charged position seen in FIG. 6 charging the spring 95 between the spring supports 93, 97. When the rod 89 and spring 95 reach the overcenter position, the pin 87 engages the projection 83 on the latch 55 to move the latch 55 from the latch position seen in FIG. 5 to the unlatched position seen in FIG. 6. With the latch 55 in the unlatched position releasing the operating shaft 41, the charged spring 95 discharges moving the pin 87 from the spring charged open position seen in FIG. 6 to the spring-discharged closed position seen in FIG. 7. During this movement the pin 87, engaging the arm portion 73, rotates the member 57, and the operating shaft 41 to which the member 57 is secured, from the open position of the operating shaft 41 (FIGS. 5 and 6) to the closed position of the operating shaft 41 (FIG. 7) with a snap action. As the operating shaft 41 moves from the open position (FIGS. 5 and 6) to the closed position (FIG. 7) the contact arms 19 are moved from the open position seen in full lines in FIG. 5 to the closed position shown in broken lines in FIG. 5 in the same manner as was hereinbefore described.

As can be understood with reference to FIG. 7, the member 57 comprises a cam surface 100 that engages the free end of the latch member 55 to hold the latch member in the upper unlatching position seen in FIG. 7 to permit movement of the pin 87 past the projection 83 on the latch member 55 during the opening operation of the circuit interrupter. When the circuit interrupter is operated to the open position the spring 79 automatically moves the latch member 55 into latching engagement with the latch surface 75.

The circuit interrupter is opened by reverse movement of the operating handle 61 from the closed position seen in FIG. 7 to the open position seen in FIG. 5. During this movement the arm portion 69 of the drive means 51, engaging the pin 87, drives the overcenter spring structure 53, with the member 85 moving in a counterclockwise direction on the shaft 41, to charge the spring 95. When the overcenter spring structure 53 reaches the overcenter position the charged spring 95 discharges to drive the overcenter spring structure 53 to the fully open position seen in FIG. 5. During this discharging movement, the pin 87, engaging the arm portion 71 of the member 57, drives the member 57 and the operating shaft 41 to which the member 57 is secured, in a counterclockwise direction from the closed position seen in FIG. 7 to the open position seen in FIG. 5. During movement of the operating shaft 41 to the open position the contact arms 19 (FIG. 4) are driven from the closed position seen in broken lines in FIG. 5 to the open position seen in full lines in FIG. 5 with a snap action in the same manner as was hereinbefore described.

Referring to FIG. 4, it will be noted that when the circuit interrupter is in the open position the weight of the contact arms 19 tends to move the contact arms 19 in a clockwise direction toward the closed position. When the overcenter spring structure 53 is in the spring discharged open position (FIG. 5) this clockwise movement of the contact arms 19 (FIG. 4) would be prevented by the engagement of the arm 71 (FIG. 5) with the pin 87 of the overcenter spring structure 53 even if a latch 55 were not provided. However, if the latch 55 were not provided, during a manual operation as the overcenter spring structure is manually moved toward the spring-charged position seen in FIG. 6 the pin 87 would move away from'the arm 71 (FIG. 5) and the force of gravity operating on the contact arms 19 would cause the contact arms 19 to move slowly toward the closed position following the pin 87. Thus, the latch 55 (FIG. 5) is provided to latch the operating shaft 41 and contact arms 19 in the open position as the overcenter spring structure 53 is moved toward the spring-charged open position (FIG. 6), and when the overcenter spring structure 53 reaches its spring-charged operating position the pin 87, engaging the projection 83, automatically moves the latch 55 from the latching position seen in FIG. 5 to the unlatching position seen in FIG. 6 whereupon the overcenter spring structure 53 drives the operating shaft 41 and contact arms 19 to the closed position with a snap action.

As can be understood with reference to the closed position illustrated by broken lines in FIG. 4, when the circuit interrupter is in the closed position the force of gravity does not tend to move the contact arms 19 toward the open position. Moreover, the frictional engagement between the contact arms 19 (FIG. 1) and the stationary contacts 13, holds the contact arms 19 and operating shaft 41 in the closed position as the drive means 51 is operated from the spring discharged closed position to the spring-charged closed position during an opening operation. Thus, for some applications, it is not necessary to provide a latching function, similar to the one hereinbefore described with reference to the closing operation, during an opening operation of the circuit interrupter.

For certain installations, however, it is desirable to provide the latching function to latch the operating shaft 41 and contact arms 19 as the spring is moved to the charged overcenter position during both closing and opening operations of the circuit interrupter. For these applications, the latch means 103 (FIG. 8) is provided. The latch means 103 comprises the latch 55, and an additional latch 105 both of which are mounted for pivotal movement on the pin 77. The latch 105 is provided with a projection 107, similar to the projection 83 on the latch 55, and the member 57 is provided with a latching surface 109 similar to the latching surface 75. The spring 79 is connected between both of the latches 55, 105 to bias the latches toward each other toward latching engagement with the associated latch surfaces. In the embodiment illustrated in FIG. 8, the latch 55 functions in the same manner as was hereinbefore described during a closing operation of the circuit interrupter. The latch 105 performs a similar latching function during an opening operation of the circuit interrupter. During an opening operation of the circuit interrupter the latch 105, biased into latching engagement with the latch surface 109 by means of the spring 79, latches the operating shaft 41 and contact arms 19 in the closed position as the drive means 51 is operated from the spring discharged closed position to the overcenter spring-charged closed position. When the overcenter spring structure 53 reaches the overcenter spring-charged closed position, the pin 87 engages the projection 107 of the latch 105 to move the latch 105 to the unlatching position whereupon the overcenter spring structure 53 moves to the open position seen in FIG. 5 and the pin 87, operating against the arm portion 71, drives the operating shaft 41 and contact arms 19 to the open position in the same manner as was hereinbefore described. When the circuit interrupter is operated to the open position the cam surface 100 on the member 57 engages the free end of the latch member 105 to hold the latch down permitting the pin 87 to move past the projection 107 on the latch member 105 during the closing operation of the circuit interrupter. As can be understood with reference to FIG. 8, the latches 55 and 105 are automatically moved to their respective latching positions during operation of the operating shaft 41. Although the additional latch is not necessary for all applications because of the frictional engagement between the contact arms 19 and stationary contacts 13, for certain installations where shock conditions may occur or where it is desirable to increase assurance against a slow opening operation, the latch 105 can be readily used in the circuit interrupter in combination with the latch 55.

What I claim is:

l. A circuit interrupter comprising a stationary contact structure, a movable contact structure cooperable with said stationary contact structure, an operating shaft pivotally movable between open and closed positions to move said movable contact structure between open and closed positions, an overcenter spring structure comprising an overcenter spring and being movable in one direction from a spring discharged open position to a spring charged open position to charge said overcenter spring and thereafter said charged overcenter spring discharging to move said overcenter spring structure from said spring charged open position to a spring discharged closed position to move said operating shaft to the closed position, said overcenter spring structure being movable in another direction from said spring discharged closed position to a spring charged closed position to charge said overcenter spring and thereafter said charged overcenter spring discharging to move said overcenter spring structure from said spring charged closed position to a spring discharged open position to move said operating shaft to the open position, manually operable drive means supported on said operating shaft for pivotal movement on said operating shaft relative to said operating shaft, said manually operable drive means being manually operable in a first direction to move said overcenter spring structure from said spring discharged open position to said spring charged open position, said manually operable drive means being movable in a second direction to move said overcenter spring structure from said spring discharged closed position to said spring charged closed position, a latch part fixed to said operating shaft and movable unitarily with said operating shaft, a latch member operating automatically when said operating shaft is in said open position to engage said latch part to latch said operating shaft in said open position, and said drive means moving said latch member to unlatch said operating shaft when said overcenter spring structure is moved to said spring charged open position.

2. A circuit interrupter according to claim 1, said latch member being mounted on a fixed pivot for pivotal movement between latching and unlatching positions, and spring means biasing said latch member into latching position latching said operating shaft in said open position.

3. A circuit interrupter according to claim 2, said drive means engaging said latch member to move said latch member against the bias of said spring means to the unlatching position to unlatch said operating shaft when said overcenter spring structure is moved to said spring charged open position.

4. A circuit interrupter comprising a stationary contact structure, a movable contact structure cooperable with said stationary contact structure, an operating shaft pivotally movable between open and closed positions to move said movable contact structure between open and closed positions, an overcenter spring structure comprising an overcenter spring and being movable in one direction from a spring discharged open position to a spring charged open position to charge said overcenter spring and thereafter said charged overcenter spring discharging to move said overcenter spring structure from said spring charged open position to a spring discharged closed position to move said operating shaft to the closed position, said overcenter spring structure being movable in another direction from said spring discharged closed position to a spring charged closed position to charge said overcenter spring and thereafter said charged overcenter spring discharging to move said overcenter spring structure from said spring charged closed position to a spring discharged open position to move said operating shaft to said open position, manually operable drive means supported on said operating shaft for pivotal movement on said operating shaft relative to said operating shaft, said manually operable drive means being manually operable in a first direction to move said overcenter spring structure from said spring discharged open position to said spring charged open position and in a second direction to move said overcenter spring structure from said spring discharged closed position to said spring charged closed position, latch surface means on said operating shaft movable unitarily with said operating shaft, latch means operating automatically when said operating shaft is in said open position to engage said latch surface means to latch said operating shaft in said open position, said drive means moving said latch means to unlatch said operating shaft when said overcenter spring structure is moved to said spring charged open position, said latch means operating automatically when said operating shaft is in said closed position to engage said latch surface means to latch said operating shaft in said closed position, and said drive means moving said latch means to unlatch said operating shaft when said overcenter spring structure is moved to said spring charged closed position.

5. A circuit interrupter according to claim 4, said latch means comprising a pair of separate latch members mounted on a fixed pivot and spring means biasing said latch members toward each other toward latching positions, a first of said latched members operating automatically when said operating shaft is in said open position to latch said operating shaft in said open position, and the second of said latch members operating automatically when said operating shaft is in said closed position to latch said operating shaft in said closed position, said drive means moving said first latch member to unlatch said operating shaft when said overcenter spring structure is moved to said spring charged open position, and said drive means moving said second latch member to unlatch said operating shaft when said overcenter spring structure is moved to said spring charged closed position. 

1. A circuit interrupter comprising a stationary contact structure, a movable contact structure cooperable with said stationary contact structure, an operating shaft pivotally movable between open and closed positions to move said movable contact structure between open and closed positions, an overcenter spring structure comprising an overcenter spring and being movable in one direction from a spring discharged open position to a spring charged open position to charge said overcenter spring and thereafter said charged overcenter spring discharging to move said overcenter spring structure from said spring charged open position to a spring discharged closed position to move said operating shaft to the closed position, said overcenter spring structure being movable in another direction from said spring discharged closed position to a spring charged closed position to charge said overcenter spring and thereafter said charged overcenter spring discharging to move said overcenter spring structure from said spring charged closed position to a spring discharged open position to move said operating shaft to the open position, manually operable drive means supported on said operating shaft for pivotal movement on said operating shaft relative to said operating shaft, said manually operable drive means being manually operable in a first direction to move said overcenter spring structure from said spring discharged open position to said spring charged open position, said manually operable drive means being movable in a second direction to move said overcenter spring structure from said spring discharged closed position to said spring charged closed position, a latch part fixed to said operating shaft and movable unitarily with said operating shaft, a latch member operating automatically when said operating shaft is in said open position to engage said latch part to latch said operating shaft in said open position, and said drive means moving said latch member to unlatch said operating shaft when said overcenter spring structure is moved to said spring charged open position.
 2. A circuit interrupter according to claim 1, said latch member being mounted on a fixed pivot for pivotal movement between latching and unlatching positions, and spring means biasing said latch member into latching position latching said operating shaft in said open position.
 3. A circuit interrupter according to claim 2, said drive means engaging said latch member to move said latch member against the bias of said spring means to the unlatching position to unlatch said operating shaft when said overcenter spring structure is moved to said spring charged open position.
 4. A circuit interrupter comprising a stationary contact structure, a movable contact structure cooperable with said stationary contact structure, an operating shaft pivotally movable between open and closEd positions to move said movable contact structure between open and closed positions, an overcenter spring structure comprising an overcenter spring and being movable in one direction from a spring discharged open position to a spring charged open position to charge said overcenter spring and thereafter said charged overcenter spring discharging to move said overcenter spring structure from said spring charged open position to a spring discharged closed position to move said operating shaft to the closed position, said overcenter spring structure being movable in another direction from said spring discharged closed position to a spring charged closed position to charge said overcenter spring and thereafter said charged overcenter spring discharging to move said overcenter spring structure from said spring charged closed position to a spring discharged open position to move said operating shaft to said open position, manually operable drive means supported on said operating shaft for pivotal movement on said operating shaft relative to said operating shaft, said manually operable drive means being manually operable in a first direction to move said overcenter spring structure from said spring discharged open position to said spring charged open position and in a second direction to move said overcenter spring structure from said spring discharged closed position to said spring charged closed position, latch surface means on said operating shaft movable unitarily with said operating shaft, latch means operating automatically when said operating shaft is in said open position to engage said latch surface means to latch said operating shaft in said open position, said drive means moving said latch means to unlatch said operating shaft when said overcenter spring structure is moved to said spring charged open position, said latch means operating automatically when said operating shaft is in said closed position to engage said latch surface means to latch said operating shaft in said closed position, and said drive means moving said latch means to unlatch said operating shaft when said overcenter spring structure is moved to said spring charged closed position.
 5. A circuit interrupter according to claim 4, said latch means comprising a pair of separate latch members mounted on a fixed pivot and spring means biasing said latch members toward each other toward latching positions, a first of said latched members operating automatically when said operating shaft is in said open position to latch said operating shaft in said open position, and the second of said latch members operating automatically when said operating shaft is in said closed position to latch said operating shaft in said closed position, said drive means moving said first latch member to unlatch said operating shaft when said overcenter spring structure is moved to said spring charged open position, and said drive means moving said second latch member to unlatch said operating shaft when said overcenter spring structure is moved to said spring charged closed position. 